Patent GB-860847-A (GB)
Abstract: 860,847. Electric indicating systems. HOFMANN, D., and HOFMANN, R., [trading as GEBRUDER HOFMANN KOMM - GES.]. June 11, 1957 [June 11, 1956], No. 18435/57. Class 40 (1). Apparatus for determining the magnitude and angular position of the unbalance of a rotor comprises a pressure transducer whose signals are chopped into two trains by suppressing periods of 180 degrees displaced by 90 degrees, the two trains being integrated and combined in a manner to produce an A.C. signal of a predetermined frequency having the same amplitude and phase relative to a fixed control voltage. Mechanical chopping arrangement (Fig. 1). The unbalance of a rotor 2 is sensed by a moving coil transducer 5, amplified at 6 and fed to synchronously rotating switch discs 7, 8, each closing a circuit for 180 degrees in each revolution, the two closures being displaced by 90 degrees. Each of the two signal trains so produced is fed through an R.C. integrator 13, 15 and 14, 16 to produce D.C. voltages M1, M2 on capacitors 15, 16 proportional to the average value of each pulse train. The voltages are split into rectangular pulse trains by rotating discs 23, 24 driven at an independent speed by motor 21, and the output pulse trains, having equal mark-space durations with a phase displacement of 90 degrees, are fed through valves 26<SP>1</SP>, 27<SP>1</SP> to be combined by resistors 29, 29<SP>1</SP> and fed through a filter 30 tuned to the frequency corresponding to the speed of motor 21, whereby the fundamental only is allowed through. The amplitude, which is indicative of the magnitude of the unbalance, is shown on a meter 31, and the phase angle is determined by comparing the fundamental with a pulse train derived from a D.C. voltage chopped by a rotating switch disc 25, and is indicative of the phase of the unbalance signal from transducer 5. Electronic chopping arrangement (Fig. 9). The unbalance signal developed in winding 41 is amplified at 50, 58 and fed to electronic switching circuits comprising pairs of valves 74, 75 and 84, 85, the valves of each pair being connected in parallel opposition, the grids being fed with trains of rectangular pulses obtained as follows. Windings 90, 91 wound on magnets are located diametrically opposite each other with respect to the shaft driving the test rotor carrying an iron insert or peg whereby a pulse is generated in each winding 90, 91 as the iron part passes the coil. The negative part of the pulse in winding 90 is by-passed by a diode 92, and the positive part of the pulse in winding 91 is by-passed by a diode 93. The pulse trains are now combined to give alternate positive and negative pulses spaced by 180 degrees, and fed to a multivibrator pair 100, 101 to produce a train of rectangular pulses with equal mark-space durations, which is fed to the grids of valves 74, 75. The rectangular pulse train is also fed to a second multivibrator pair 113, 114 through an R.C. integrator circuit 111, 112 to produce a second rectangular pulse train similar to the first train but displaced by 90 degrees. This train is fed to the grids of valves 84, 85. The rectangular pulses cause the valves 74, 75, 84, 85 to fire for the duration of each pulse, and the signals from winding 41 are suppressed during this time, the half-signals which pass through being integrated at 73, 79 and 83, 89 to give the voltages M1, M2 across capacitors 79, 89 respectively, which can be isolated from the preceding apparatus by opening switches 78, 88. Each voltage M1, M2 is fed to a pair of valves 120 121 and 130, 131, the valves of each pair being connected in parallel opposition with the grids fed with control pulses obtained from the supply mains as follows. The voltage at one end 152 of the secondary winding of a mains transformer 150 is clipped by diodes 156, 157 to supply a trapezoidal control voltage to the grids of valves 120, 121. A similar trapezoidal control voltage displaced by 90 degrees is obtained from the junction of capacitor 160 and resistor 161 after clipping by diodes 166, 167, and is fed to the grids of valves 130, 131. Thus the valve pairs 120, 121 and 130, 131 pass on trains of rectangular pulses of equal mark-space durations with a phase difference of 90 degrees, the amplitudes being M1, M2 respectively and whose repetition frequency is that the supply whose repetition frequency is that of the supply mains. The pulse trains are combined by capacitors 125, 135 and fed through amplifier valves 140, 142 containing a resonance circuit 143 tuned to the mains frequency, the fundamental frequency component being passed on via cathode-follower 141 to be shown on a meter 145 as indicative of the magnitude of the unbalance of the rotor 2. To determine the phase of the unbalance, the sine wave voltage at mains frequency across meter 145 is also fed to a multivibrator 170, 171 to produce corresponding square waves which are differentiated by capacitor 172 and resistor 173, the resulting positive pulses being by-passed by diode 174 and the negative pulses being fed to the grid of one valve 175 of a flip-flop circuit. The other valve 176 of the flip-flop is fed with negative pulses derived from the mains transformer 150, after squaring at 179 and differentiating at 180, 181, the positive pulses being by-passed by diode 182. Each pulse from the alternate trains causes the flip-flop to change over, so that the duration of anode current in valve 175 is indicative of the phase difference between the two trains, and is shown by a meter 183 reading average current.